The present invention relates to a process for producing pellets which comprise active compounds and are based on thermoplastic polymers by melt extrusion and underwater pelletizing and also relates to corresponding pellets and their use.
Underwater pelletizing is generally known as an effective pelletizing method for thermoplastic materials for the industrial production of plastic pellets.
Corresponding apparatuses and processes are described, for example, in DE-A 2646309, U.S. Pat. No. 4,264,553 or U.S. Pat. No. 5,143,673. In these the hot plastic melt is transported from an extruder via a perforated disk directly into a liquid cooling medium, in this case water. The exiting plastic strands are divided into pellets by a cutting apparatus mounted at the perforated disk and are transported away by the generally recirculated water, separated off and dried. By means of this liquid-cooled process it is possible to produce very small particle sizes uniformly, continuously and on an industrial scale down to the submillimeter range. By using cooling media having a high heat capacity and a high heat transfer, such as water, the still-plastic pellets are rapidly cooled, do not stick together and may be produced in very uniform shape and size.
In comparison, using die-face cutting with air cooling for pelletizing the extruded strands is considerably more difficult because of the slow and poor heat transfer.
Formulations which contain active compounds, for example comprising vitamins as active compound, are administered, to maintain the health of humans and animals, in parallel to food intake or are added to the diet as additive. A large proportion of the formulations of vitamins, vitaminoids or other food supplements manufactured is required for animal nutrition. Since the feedstuffs used there are supplied as ground material having a mean particle size of 0.3-0.5 mm, added feed additivesxe2x80x94to prevent separationxe2x80x94should have roughly the same size and uniformity. Uniform particle size is also of particular importance for producing pellets for drugs, since the dissolution behavior and thus the bioavailability are dependent on the particle size. The previously used drug pellets, feed supplements or feed additives are therefore usually produced in complex and expensive grinding, pelletizing and spraying processes.
Preparations which contain active compounds and are produced by melt extrusion are generally known. Extrusion of melts of water-soluble polymers, which melts contain active compounds, preferably copolymers of vinylpyrrolidone, is disclosed, for example, by EP-A 240904 and EP-A 240906. EP-A 240 906 also describes the melt extrusion of active-compound-containing mixtures, copolymers of methyl methacrylate and acrylic acid, copolymers of vinyl acetate and crotonic acid, and also ethylene/vinyl acetate copolymers. They are shaped via injection molding or extrusion with subsequent shaping of the still-plastic strand, for example by die-face cutting to form pellets or shaping to form tablets. In all said examples shaping is performed in air. The pharmaceutical forms thus produced are generally water-soluble.
Thus, for example, DE-A 19536387 also describes melt extrusion and shaping of vitamin-containing products. Water-soluble, thermoplastic hydroxypropylcelluloses are used as matrix. In the examples, inter alia, melts of vitamin C or xcex2-carotene together with hydroxypropylcellulose are pressed by shaping calenders to form tablets. In addition, die-face cutting of the water-soluble matrix to form pellets is mentioned.
Although such water-soluble formulations can be produced using melt extrusion and subsequent pelletizing in air, it is a disadvantage that frequently, owing to the poor heat transfer, the required (small) particle size, uniformity and large-scale feasibility cannot be achieved in this manner.
It is an object of the present invention to develop an inexpensive and simple production process for formulations which contain active compounds, for example drugs or feed additives, which dissolve or disperse on their own in water or in the gastrointestinal tract.
We have found that this object is achieved, surprisingly, if mixtures which comprise active compounds are melt-extruded with polymers which are water-insoluble in a certain pH range and are water-soluble in another pH range.
Accordingly, a process was found for producing pellets which comprise biologically active substances in which the biologically active substances are homogeneously dispersed in a matrix based on at least one thermoplastic polymer, which polymer has in aqueous medium a pH-dependent solubility, by homogeneous mixing of the starting materials in the melt and subsequent extrusion and shaping, which comprises the shaping being performed in a cooling medium in which the pellets are not soluble or dispersible.
To carry out the process of the invention, the starting materials are mixed to form a homogeneous melt. This can be done, for example, by introducing a physical premix of solid starting materials into a suitable extruder or kneader, melting the mixture with the use of mechanical and thermal energy, and transporting the hot, still-plastic melt through a perforated disk or a nozzle plate directly into a liquid cooling medium. If the formulation also comprises liquid constituents, it is advisable to add these separately via a metering pump. If thermally labile active compounds are used, it can also be advisable firstly to prepare a melt of the thermoplastic polymers and, if desired, other formulation aids, and only then to add the active compound. The melting is preferably performed in a screw machine, in particular in a double-screw extruder, which is preferably corotating. The process of the invention is preferably carried out in the absence of solvents. In the event that it should be necessary to add to the mixture one or more of the starting materials in the form of a solution, the solvents used here can be removed in the downstream extruder zones by applying a vacuum. The extruded, still-thermoplastic mass then no longer contains solvent.
The starting materials can be melted, depending on composition of the mixture, at from 50 to 300xc2x0 C., preferably from 70 to 250xc2x0 C.
The exiting plastic strands are divided into pellets by a cutting apparatus mounted at the perforated disk or nozzle plate, and are transported away by the preferably recirculated cooling medium, separated off and dried. Suitable cooling media are, for example, liquid hydrocarbons such as paraffins or aromatic hydrocarbons, or preferably water. If water is used as cooling medium, according to the invention the pH of the water is set using acids or bases such that the matrix comprising the active compounds does not dissolve or disperse itself therein. According to the invention this is intended to mean that no more than 1 g/l of the pellets may be dissolved or dispersed in water.
By using cooling media having a high heat capacity and a high heat transfer, such as water, the still-plastic pellets are rapidly cooled, do not stick together and may be produced in very uniform shape and size. Preference is given to pellets produced having mean particle sizes of from 0.1 to 5, preferably from 0.3 to 3, mm.
The process of the invention is suitable in principle for producing pellets comprising biologically active substances in which one or more biologically active substances is/are homogeneously dispersed in a matrix based on thermoplastic polymers. Homogeneously dispersed can also mean according to the invention that the biologically active substances are present molecularly dispersed in the matrix, that is are what are termed xe2x80x9csolid solutionsxe2x80x9d.
Biologically active substances which can be used are generally all substances which are to be released in the gastrointestinal tract of humans and animals. These can be, for example, active drug compounds, vitamins, vitaminoids, carotenoids, enzymes, hormones, amino acids or xe2x80x9cnutraceuticalsxe2x80x9d, that is to say food supplements and dietetic compositions.
In addition, it is also possible to formulate active plant protection compounds, laundry detergent constituents, odorants and flavorings or other active substances in the above-described manner.
The process of the invention and the apparatus of the invention are suitable for preparing particulate preparations of biological substances. Biologically active substances are according to the invention substances which cause a biological effect in living organisms.
The process of the invention is suitable, for example, for formulating the following substances or their physiologically acceptable salts, in which case the salts can also be produced in situ in the extruder:
Antiinfective Compositions
Aciclovir, aminoglycosides, amphotericin B, azole-antimycotics, clotrimazole, itraconazole, sepraconazole, clindamycin, cephalosporins, chloramphenicol, erythromycin, 5-fluorouracil, etoposide, flucytosine, ganciclovir, griseofulvin, gyrase inhibitors, isoniazid, lincosamides, mebendazole, mefloquine, metronidazole, nitroimidazoles, novobiocin, platinum compounds, polymyxin B, praziquantel, pyrimethamine, rifampicin, saquinavir, streptomycin, sulfonamides, tetracyclines, trimethoprim, vancomycin, zidovudine;
Antipyretics, analgesics, antiinflammatories, paracetamol, ibuprofen, ketoprofen, oxaprozin, acetylsalicylic acid, morphine, oxaprozin, propoxyphene, phenylbutazone;
Antibiotics
Rifampicin, griseofulvin, chloramphenicol, cycloserine, erythromycin, penicillins, such as penicillin G, streptomycin, tetracycline;
Antiepileptics
Hydantoins, carbamazepine;
Antitussives und Antiasthmatics
Diphenhydramine;
Antirheumatics
Chloroquine, indomethacin, gold compounds, phenylbutazone, oxyphenylbutazone, penicillamine;
Hypnotics
Barbiturates, phenobarbital, zolpidem, dioxopiperidines, ureides;
Insecticides
Aldrin, dieldrin, chlorphenotan, hexachlorocyclohexane;
Herbicides
Vinclozolin, strobilurines;
Antipsychotics, Neuroleptics
Perazine, promazine, sulpiride, thioridazine, chlorpromazine, meprobamate, triflupromazine, melperone, clozapine, risperidone, reserpin;
Tranquillizers;
Antidepressives
Imipramine, paroxetine, viloxazine, moclobemide;
Psychotonics;
Psychomimetics;
Diuretics
Potassium canrenoate, loop diuretics, furosemide, hydrochlorothiazide, spironolactone, thiazides, triamterene;
Hormones
Androgens, antiandrogens, gestagens, glucocorticoids, oestrogens, cortisol, dexamethasone, prednisolone, testosterone, Adiuretin, oxytocin, somatropin, insulin;
Immunosuppressants
Cyclosporin;
Bronchodilators;
Muscle Relaxants, Tranquillizers
Carisoprodol, tetrazepam, diazepam, chlordiazepoxide;
Enzymes
Lipase, phytase;
Antigouts
Allopurinol, colchicine;
Anticoagulants
Coumarins;
Antiepileptics
Phenytoin, phenobarbital, primidone, valproic acid, carbamazepine;
Antihistamines
Chlorphenoxamine, dimenhydrinate;
Antiemetics;
Antihypertensives, Antiarrhythmics
Lidocaine, procainamide, quinidine, calcium antagonists, glycerol trinitrate, isosorbide dinitrate, isosorbide 5-mononitrate, pentaerythrityl tetranitrate, nifedipine, diltiazem, felodipine, verapamil, reserpine, minoxidil, reserpiline, captopril, enalapril, lisinopril;
Sympathomimetics
Norfenefrine, oxedrine, midodrine, phenylephrine, isoprenaline, salbutamol, clenbuterol, ephedrine, tyramine, xcex2-blockers such as alprenolol, metoprolol, bisoprolol;
Antidiabetics
Biguanides, sulfonylureas, carbutamide, tolbutamide, glibenclamide, metformin, acarbose, troglitazone;
Iron preparations;
Vitamins and Vitaminoids
For example ascorbic acid, tocopherol, tocopherol acetate, vitamin A and vitamin A derivatives, vitamin K and vitamin K derivatives or vitamin D and vitamin D derivatives, riboflavin, vitamin B12, nicotinic acid, nicotinamide, pyridoxin hydrochloride, biotin, folic acid, folic acid derivatives, such as tetrahydrofolic acid, 5-methyltetrahydrofolic acid, 10-formyltetrahydrofolic acid or 5-formyltetrahydrofolic acid;
carotenoids, for example xcex2-carotene, lycopene, lutein, astaxanthin or zeaxanthin;
polyunsaturated fatty acids, for example linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid or eicosapentaenoic acid;
compounds having vitamin character or coenzyme character, for example carnitine, choline chloride, taurine, creatine, ubiquinones, S-methylmethionine or S-adenosylmethionine;
ACE Inhibitors
Captopril, ramipril, enalapril;
Anabolics;
Iodine compounds;
X-ray contrast materials;
Compounds having CNS activity;
Antiparkinsonians
Biperiden, benzatropine, amantadine, opioid analgesics, barbiturates, benzodiazepines, disulfiram, lithium salts, theophylline, valproinate, neuroleptics;
Cytostatics;
Antispasmolytics;
Vasodilators
Naftidrofuryl, pentoxifylline.
Preparations of the biologically active substances can also be obtained in the form of xe2x80x9csolid solutionsxe2x80x9d. The term xe2x80x9csolid solutionsxe2x80x9d is familiar to those skilled in the art (see Chiou and Riegelman, J. Pharm. Sci. 60, 1281-1302 (1971)). In solid solutions of active pharmaceutical compounds in polymers or other matrices, the active compound is present in the matrix in molecularly dispersed form.
Suitable matrix components are in principle all thermoplastic polymers which have a pH-dependent water solubility. In particular, these are polymers having acid (e.g. carboxylate) or base (e.g. amine) functionalities or having acid- or base-unstable functionalities (e.g. esters).
Polymers which can be used are, for example, the homopolymers and copolymers of N-vinylpyrrolidone, vinyl acetate being a preferred comonomer.
Suitable polymers are, for example, also copolymers of vinyl acetate and crotonic acid, for example Luviset(copyright) CA 66, BASF, a copolymer of 90% by weight of vinyl acetate and 10% by weight of crotonic acid. Similarly suitable are copolymers of methacrylic acid and ethyl acrylate, for example Kollicoat(copyright) MAE 100 P, BASF, or Luvimer(copyright) 100 P (terpolymer of 67% by weight of t-butyl acrylate, 23% by weight of methacrylic acid and 10% by weight of ethyl acrylate) from BASF, and in addition non-hydrolyzed or partially hydrolyzed polyvinyl acetates, for example the Vinnapas brands (up to 100% vinyl acetate) from Wacker, and, for example, dimethylaminoethyl acryl ate copolymers.
Preferably, polymers are used which contain, as comonomers, monoolefinically unsaturated carboxylic acids which can be polymerized in a free-radical manner, for example acrylic acid, methacrylic acid or crotonic acid.
Additional comonomers which are preferably used are monoolefinically unsaturated carboxylic esters having up to 6 carbon atoms, for example methyl, ethyl, n-butyl or tert-butyl methacrylate, methyl, ethyl, n-butyl or tert-butyl acrylate, vinyl acetate and vinyl propionate.
Particular preference is given to polymers which contain at least 30% by weight of acrylic acid or methacrylic acid as comonomer. In addition, terpolymers containing, for example, dimethylaminoethyl acrylate and derivatives, butyl esters or acrylamides can also be used.
Particular preference is given to matrices comprising biologically active substances and polymers, which matrices, if desired, additionally comprise plasticizers and other formulation aids, and dissolve or disperse in water or aqueous systems at a pH of  greater than 5, so that a solid dosage form of the respective formulation sufficiently rapidly and completely releases the active substance into the gastrointestinal tract of animals or humans. At pHs of  less than 3, these formulations should not be soluble or dispersible, or should be significantly more poorly soluble or dispersible, in water or aqueous systems. This is the case, for example, with the use of hydrophobic active substances such as vitamin A with matrix polymers of acrylic acid or methacrylic acid and acrylic esters (methacrylic and acrylic esters) having an acrylic acid or methacrylic acid content of xe2x89xa730%. However, the release rate depends in each case on the polymer matrix used, the plasticizers optionally used and on other additives, and also on the active substance.
In addition to polymer and active compound, formulations of this type can comprise customary additives relating to extrusion and formulation, for example plasticizers and stabilizers.
Plasticizers which are used are, for example, polyethylene glycols, triacetin, triethyl citrate or propanediol.
Stabilizers, Surfactants etc. and Extrusion Aids
Depending on field of application and processability, the contents of active compound, polymer and additives can vary within broad ranges. The sole boundary conditions are the thermoplastic processability and the described solubility properties of the formulation. Generally, the active compound content will be in a range from 5 to 90, preferably from 5 to 80, particularly preferably from 5 to 60% by weight. The remainder is formed by polymers, generally from 10 to 55% by weight, and formulation aids.
Using the process of the invention it is possible to produce active-compound-containing formulations by melt extrusion and underwater pelletizing in an insoluble pH range and, after separation, to redissolve these in a soluble pH range (underwater pelletizing of active-compound-containing melts having pH-dependent solubility). Manufacture using water as cooling medium is inexpensive, environmentally compatible, safe and simple, but, for reasons of product solubility, it can be necessary to use other liquid media, for example mineral oils, vegetable oils or other organic solvents. In addition, it is possible to add to the water soluble additives, for example salts, in order to decrease the solubility of the formulation. Under the abovementioned conditions, with the choice of matrices, recourse no longer has to be made to pH-dependent solubilities. For example, it is conceivable to pelletize an active-compound-containing matrix of the water-soluble nonionic polymer polyvinylpyrrolidone or cellulose derivatives or VP copolymers in a hydrocarbon as cooling medium. Polyvinylpyrrolidine is virtually insoluble in paraffins. These products could then re-release the active substance in water.
Thus, it is for example possible to pelletize a polymeric thermoplastic matrix of methacrylic acid and ethyl acrylate at pHs of 3-4 under water and, after the separation, to dissolve the resultant pellets in water at pHs of 7-8. The dissolution properties of the overall formula are codetermined by the active compounds, plasticizers and additives used.
The pellets of the invention are suitable in particular for use in feedstuffs, food supplements or dietetic compositions, and in addition for producing drugs for the human and veterinary sector and for plant protection compositions.
The pellets are also suitable for laundry detergent formulations which comprise enzymes or aroma substances as biologically active substances.
The pellets can be used as such. In addition, they are suitable as capsule fillings or for pressing to form tablets.